How to Sort 2D ArrayList by Only the First Element [duplicate]

Answer 1

Create a custom comparator:

final Comparator<List<String>> comparator = new Comparator<List<String>>() {
    public int compare(List<String> pList1, List<String> pList2) {
        return pList1.get(0).compareTo(pList2.get(0));
    }
};
final List<List<String>> lists = Arrays.asList(
    Arrays.asList("Mike", "(805) 766-4920"),
    Arrays.asList("Emily", "(705) 668-9292", "(705) 555-1060"),
    Arrays.asList("James", "(605) 965-2000")
);
Collections.sort(lists, comparator);
for (List<String> list : lists) System.out.println(list);

Answer 2

For diversity Why dont you just use a HashMap unless you want duplicate keys. the key would be name and the value would be an ArrayList of numbers

String name="John";

ArrayList<String> phonenumbers=new ArrayList<String>();

phonenumbers.add("80925887");
phonenumbers.add("+166476654");

TreeMap<String, ArrayList> tm=new TreeMap<String, ArrayList>();

tm.put(name, phonenumbers);

Answer 3

You can use Collections.sort and provide a custom Comparator where you compare the first element of each list, i.e the name :

List<ArrayList<String>> namesAndNumbers = new ArrayList<ArrayList<String>>();
namesAndNumbers.add(new ArrayList<String>(Arrays.asList("Mike", "(805) 766-4920")));
namesAndNumbers.add(new ArrayList<String>(Arrays.asList("Emily", "(705) 668-9292", "(705) 555-1060")));
namesAndNumbers.add(new ArrayList<String>(Arrays.asList("James", "(605) 965-2000")));
Collections.sort(namesAndNumbers, new Comparator<ArrayList<String>>() {    
        @Override
        public int compare(ArrayList<String> o1, ArrayList<String> o2) {
            return o1.get(0).compareTo(o2.get(0));
        }               
});
System.out.println(namesAndNumbers);

Output :

[[Emily, (705) 668-9292, (705) 555-1060], [James, (605) 965-2000], [Mike, (805) 766-4920]]